This invention belongs to the broad class of dampers and absorbers which utilize visco-elastic elements, but, whereas many visco-elastic dampers also include an auxiliary mass, forming a tuned damper system, the present invention does not include an auxiliary mass. Also, many prior art systems for attenuating vibrations require the condition that the damped object be somehow fully supported on visco-elastic elements, so that the entire object is free to move. In contradistinction, the present invention comprises a system where one portion of a workpiece is tightly clamped to a machine base, and another portion of the workpiece, cantilevered from the clamped portion, is then intimately contacted by a visco-elastically supported pad. The invention is especially useful in those applications where the overhang is irregular or not otherwise readily supportable by conventional props and supports.
The use of visco-elastic elements in machine members is well-known. For example, U.S. Pat. No. 3,522,864 of R. C. Richter, Aug. 4, 1970, entitled Tuned Damper Assembly for Machine Tools, illustrates a tuned damper applied to machine tools, where a machine element is fitted with an annular visco-elastic absorber element. A damper mass is mounted onto, and preloaded against, the absorber element by springs and bolts.
U.S. Pat. No. 3,692,370, of J. R. Hasz, Sep. 19, 1972, entitled Damping Means For Increasing the Minimum Stiffness of a Shaft, teaches increasing the minimum dynamic stiffness of a spindle by having a sleeve of visco-elastic material bonded to the spindle between the spindle supports. A rigid sleeve surrounds the visco-elastic sleeve to constrain the visco-elastic material and increase its shear strains.
An example of the use of visco-elastic elements in a tool support is found in U.S. Pat. No. 5,033,340, of L. T. Siefring, Jul. 20, 1991, entitled Apparatus and Method for Tool Vibration Damping, where alternate layers of visco-elastic solid material and steel are layered to produced a damping sandwich at the joint in the machine tool between the cutting tip and the tool mounting area.
U.S. Pat. No. 5,040,764, of N. J. DuBois, Aug. 20, 1991, entitled Low Frequency Vibration Absorber, teaches a mounting assembly for absorbing low frequency vibrational energy produced by a source that is mounted to a base member. The mount comprises soft, spongy material, preferably foam material, to provide isolation.
An example of a workpiece damper used when machining is found in U.S. Pat. No. 4,438,599 of J. T. Kamman et al, Mar. 27, 1984, entitled Vibration Damper for Machine-carried Workpiece. Here, a slender, rotary workpiece is supported at both ends. A shoe contacts the rotating workpiece, and the blocky shoe is supported in a retractable shoe holder by a pair of elastomeric elements, oppositely disposed and preloaded against each other; the shoe is then preloaded against the workpiece in a direction transverse to the preload direction of the opposed elastomeric elements.
Th problems inherent in machining a workpiece which, at one portion, is fully clamped to a machine table, and yet, which has an overhanging portion, capable of free vibration, are obviated by the present invention.